Lebanese army deployed in the town of Arsal along the border with Syria, reopening the main road linking the town to the rest of Lebanon after a night of violent protests.
The mainly Sunni town had been sealed off by residents from the mostly-Shia neighbouring town of Labweh, where one person was killed last week by rocket fire.
The closure of the main road out of Arsal prompted fury among Sunnis in other parts of Lebanon, and many took to streets across the country on Tuesday night to burn tires in protest.
In the wake of the tensions, President Michel Sleiman was meeting on Wednesday with Prime Minister Tammam Salam and top security officials, the official National News Agency reported.
Residents of Labweh blame Sunni Arsal for the rocket fire, although it was reported to have originated across the border in Syria.
Tensions between residents of the two towns have increased since the fall of the Syrian rebel bastion Yabroud, just across the frontier, on Sunday.
Yaborud's capture prompted an exodus of hundreds of Syrians to Arsal, where residents are sympathetic towards the Syrian uprising.
Angry Sunnis during the night blocked roads in Beirut, along the coast and in the Beqaa valley to protest what they called a "siege" of Arsal by Labweh residents.
The unrest led to the death of one man and the injury of four others in a Beirut suburb.
The army reacted on Tuesday night by announcing it would deploy in the northern Beqaa border area, "particularly in the areas of Arsal and Labweh and inside them".
It said it would open the roads between the towns and work to "maintain security and stability in the region".
The deployment began deploying in the early hours of Wednesday, Arsal municipal council member Bakr Houjairi told AFP news agency.
"The army arrived around 5:00am, they have deployed in Arsal and they have opened the road leading out of the town towards Labweh," he said.
"So far the situation is very calm, we will see what will happen later, but we are happy to see the army here and opening the road up."
The conflict in neighbouring Syria has exacerbated existing sectarian tensions in Lebanon, particularly between Sunni and Shia residents.
Many Sunni Lebanese back the Sunni-dominated Syrian uprising, while many Shia support Lebanon's powerful Hezbollah movement, which is allied with Syria's government and fighting alongside it.
The border region has become particularly fragile, with Arsal hosting some 51,000 civilian refugees and facing accusations that it allows rebel fighters to establish bases in the area around it.
On Wednesday, Syrian air force launched strikes on the outskirts of Arsal, Al Jazeera’s correspondent reported.
Warplanes belonging to President Bashar al-Assad’s army have frequently bombarded the mountainous border region.